By Turkestan, I mean the area commonly thought of as where most turkic peoples live.
By Turkestan, I mean the area commonly thought of as where most turkic peoples live. OTL Turkestan is the northernmost two thirds of the -stans. How could we get this region (not neccesarily a country) to be as big as possible?
I'm not sure what you mean here. Turkistan is generally taken to mean the are of all five -stans. To get the region as big as possible, I would suggest something different needed to happen in the Russian Revolution. There was a great deal of unity in the Turkic peoples, but unfortunately the balance of military force was with the Russian settlers.
The easiest route is a CP victory. There are a large number of CP POW's in Central Asia that were used as mercenaries by the Reds - if the CP won, you essentially have a standing army all of a sudden that could support a Turkistan and supportable through the Caucasus.
Another possible route is the Ottomans stay out of the war, then pick up the Caucasus and support their cousins across the Caspian.
Don't forget East Turkistan (i.e. Xingjiang).